Engineering cementitious composite (ECC) is a new type of fiber-reinforced material with good ductility and microcrack control capability. Because ECC does not contain coarse aggregate, shrinkage cracks are easy to appear in the early stage of molding, and its molding shrinkage can be effectively suppressed by adding an expansion agent. In this paper, shrinkage-resistatant ECC was prepared by adding high-performance calcium sulfoaluminate (HCSA) expansion agent, and the effects of HCSA on the tensile and compressive mechanical properties of ECC were investigated. The results show that when HCSA doping is 4% (mass fraction), the uniaxial tensile and compressive strength of ECC can be increased. In order to describe the mechanical properties of ECC, the uniaxial tensile and compressive behaviors of ECC were simulated based on the damage variables from the perspective of the effective stress, and the tensile damage evolution equation for ECC was proposed. The uniaxial tensile and compressive damage constitutive model of ECC was developed and implanted into the ABAQUS finite element program to simulate the tests. The results show that the proposed uniaxial damage constitutive model of ECC can better describe the mechanical behavior and damage evolution of ECC during monotonic tension and monotonic compression, and its parameters are simple and easy to calibrate.